In a communications device a grouping unit uses channel state information when mapping data bits to a plurality of different constellation groups. Each constellation group is assigned to another modulation scheme. A plurality of sub-carriers is assigned to none or one of the constellation groups and each modulation uses another one of the constellation groups. The communications device includes at least one scalable interleaver unit, wherein each interleaver unit is assigned to one of the constellation groups and interleaves the assignment of data bits mapped to each constellation group and the sub-carriers that carry a symbol information derived from the data bits. As an example, the interleaver unit performs frequency interleaving by interleaving, at constellation level, the sub-carriers that carry the symbol information.
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17. A communications device comprising:
receiving circuitry that includes:
demodulator circuitry including a plurality of qam demodulators using different constellation groups, a first group of a plurality of sub-carriers being assigned to a first constellation group of the different constellation groups and a second group of the plurality of subcarriers being assigned to a second constellation group of the different constellation groups, and each constellation group of the different constellation groups using a different demodulation scheme of a plurality of demodulation schemes, wherein
the plurality of qam demodulators include scalable de-interleaver circuitry configured to de-interleave the first group of the plurality of subcarriers that are assigned to be demodulated by a first demodulation scheme of the plurality of demodulation schemes, and to de-interleave the second group of the plurality of subcarriers that are assigned to be demodulated by a second demodulation scheme of the plurality of demodulation schemes.
1. A communications device comprising:
transmitting circuitry that includes:
grouping circuitry configured to map data bits to a plurality of constellation groups according to channel state information;
modulator circuitry configured to modulate the data bits using a plurality of modulation schemes, a first group of a plurality of sub-carriers being assigned to a first constellation group of the plurality of constellation groups and a second group of the plurality of subcarriers being assigned to a second constellation group of the plurality of constellation groups, and each constellation group of the plurality of constellation groups using a different modulation scheme of the plurality of modulation schemes; and
scalable interleaving circuitry configured to interleave the first group of the plurality of subcarriers that are assigned to be modulated by a first modulation scheme of the plurality of modulation schemes, and to interleave the second group of the plurality of subcarriers that are assigned to be modulated by a second modulation scheme of the plurality of modulation schemes.
19. A method of operating a communications device, the method comprising:
mapping data bits to a plurality of constellation groups according to channel state information;
assigning, by circuitry of the communications device, a first group of a plurality of sub-carriers to a first constellation group of the plurality of constellation groups, and a second group of the plurality of subcarriers to a second constellation group of the plurality of constellation groups according to the channel state information;
modulating, by the circuitry and for each constellation group, symbols derived from the data bits mapped to respective constellation groups onto the plurality of sub-carriers assigned to the respective constellation groups, said each constellation group of the plurality of constellation groups using a different modulation scheme of a plurality of modulation schemes; and
interleaving the first group of the plurality of subcarriers that are assigned to be modulated by a first modulation scheme of the plurality of modulation schemes, and interleaving the second group of the plurality of subcarriers that are assigned to be modulated by a second modulation scheme of the plurality of modulation schemes wherein a range of interleaving is programmed according to the channel state information.
2. The communications device of
the modulator circuitry includes a plurality of modulation circuitry portions, each modulation circuitry portion using a different one of the plurality of modulation schemes; and
the scalable interleaving circuitry includes a plurality of scalable interleaver circuitry portions, wherein each scalable interleaver circuitry portion is assigned to one of the plurality of constellation groups and is configured to interleave respective sub-carriers carrying respective symbol information derived from respective data bits.
3. The communications device of
said each scalable interleaver circuitry portion is configured to interleave the respective sub-carriers carrying the respective symbol information.
4. The communications device of
said each scalable interleaver circuitry portion is configured to interleave single data bits mapped to a respective constellation group before mapping the data bits to symbols used for addressing constellation points of the respective constellation group.
5. The communications device of
said each scalable interleaver circuitry portion is configured to interleave symbols formed by groups of data bits before mapping the symbols to the plurality of sub-carriers assigned to a respective constellation group.
6. The communications device of
control circuitry configured to program a number of the plurality of sub-carriers used by said each scalable interleaver circuitry portion according to the channel state information.
7. The communications device of
the control circuitry is further configured to control an assignment of the plurality of sub-carriers to the plurality of constellation groups according to the channel state information.
8. The communications device of
9. The communications device of
degrouping circuitry configured to combine the plurality of sub-carriers carrying symbol information for all of the plurality of constellation groups.
10. The communications device of
the plurality of constellation groups are rotated, non-orthogonal constellation groups.
11. The communications device of
the modulator circuitry includes a plurality of modulation circuitry portions, and
each modulation circuitry portion includes delay circuitry in a same signal output path.
12. The communications device of
receiving circuitry configured to de-interleave and demodulate a signal as generated by the transmitting circuitry.
13. A communications system comprising:
the communications device of
another communications device comprising:
receiving circuitry that includes:
demodulator circuitry including a plurality of qam demodulators using different constellation groups, a first group of a plurality of sub-carriers being assigned to a first constellation group of the different constellation groups and a second group of the plurality of subcarriers being assigned to a second constellation group of the different constellation groups, and each constellation group of the different constellation groups using a different demodulation scheme of a plurality of demodulation schemes, wherein
the plurality of qam demodulators include scalable de-interleaver circuitry configured to de-interleave the first group of the plurality of subcarriers that are assigned to be demodulated by a first demodulation scheme of the plurality of demodulation schemes, and to de-interleave the second group of the plurality of subcarriers that are assigned to be demodulated by a second demodulation scheme of the plurality of demodulation schemes.
14. The communications device of
15. The communications device of
16. The communications device of
18. The communications device of
each of the plurality of qam demodulators is configured to de-interleave interleaved sub-carriers that carry symbol information contained in data streams.
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Embodiments of the present invention relate to communications devices supporting adaptive OFDM (Orthogonal Frequency Division Multiplexing) using a plurality of different modulation schemes for sub-carriers. Further embodiments relate to a method of operating a communications system supporting adaptive OFDM and using a plurality of different modulation schemes for sub-carriers.
OFDM distributes data over a large number of orthogonal sub-carriers. The orthogonality of the sub-carriers allows a per-carrier demodulation at the receiver side, since at the receiver side the demodulators are prevented from considering other sub-carriers than that one they are dedicated to. OFDM provides high spectral efficiency and allows sub-carrier selection and modulation to be adapted to the transmission channel characteristics.
It is an object of the invention to provide communications devices with enhanced transmission performance and an operating method, which provides enhanced transmission performance in a communications system.
The object is achieved by the subject-matters of the independent claims. Further embodiments are specified in the dependent claims respectively. Details of the invention will become more apparent from the following description of embodiments in connection with the accompanying drawings, wherein features of the various embodiments may be combined unless they exclude each other.
The communications system 199 may be a SISO (single-input-single-output) or a MIMO (multiple-input-multiple-output) system with a first communications device 100, which includes a transmitter unit 110 employing one, two or more transmit ports 101-103, and a second communications device 200, which includes a receive unit 220 employing at least one, for example two, three or four, receive ports 201-203. A transmission channel 300 connects the transmitter unit 110 and the receive unit 220.
The first communications device 100 may be an exclusively transmitting device with transmit ports 101-103 only. According to other embodiments, the first communication device 100 is a bidirectional device including, in addition to the transmitter unit 110, a receive unit 120 which may be of the type of a receive unit 220 in the second communications device 200, wherein the ports 101-103 may be bidirectional ports. The second communications device 200 may be an exclusively receiving device. According to other embodiments, the second communications device 200 is a bidirectional device including, in addition to the receive unit 220, a transmitter unit 210 which may be of the type of the transmitter unit 110 in the first communications device 100, wherein the ports 201-203 may be bidirectional ports. The communications devices 100, 200 may be stand-alone devices or may be integrated in an electronic device for consumer applications, for example a storage unit, a television set, an audio receiver, or a video recorder.
The transmission channel 300 may be multi-wire connection. In accordance with an embodiment, the transmission channel 300 is a power cable containing two or more electrical conductors used for transmission of AC (alternating current) electric power and installed as permanent wiring within buildings or buried in the ground. For example, the transmitter unit 110 may supply two differential transmit signals using the live or phase wire (L, P), the neutral wire (N), and protective earth (PE), wherein the differential transmit signals are modulated on a carrier superposing the AC frequency of the mains voltage. According to an embodiment, the receive unit 220 receives three differential receive signals between live wire and neutral wire, between neutral wire and protective earth, and between live wire and protective earth. According to another embodiment, the receive unit 220 may receive the three differential receive signals and a common mode signal resulting from a leakage current from the wiring as a fourth receive signal.
The transmitter unit 110 may include a serial-to-parallel multiplexer unit 130 that receives the encoded data stream d2 and splits or multiplies the encoded data stream d2 into a predefined number of parallel data streams d3, wherein each data stream d3 is assigned to one of a plurality of signal paths, wherein each signal path corresponds to one of the transmit ports. In embodiments referring to SISO systems, the multiplexer unit 130 is omitted and the encoded data stream d2 is directly transmitted to a first modulator unit 150.
According to the illustrated embodiment, the parallel data streams d3 are transmitted to a first modulator unit 150. The first modulator unit 150 includes, for each signal path, a plurality of modulations. Each modulation is assigned to a constellation group, wherein each constellation group uses another modulation scheme. The modulation scheme may be any modulation from 1 bit up to x bits per carrier, for example PSK (Phase-Shift Keying), QPSK (Quadrature Phase-Shift Keying), 4-QAM (Quadrature Amplitude Modulation), 8-QAM, 64-QAM, 256-QAM, 1024-QAM, 4096-QAM, any other 2n-QAM, or any 2n-PAM (Pulse Amplitude Modulation). In dependence on the SNRs determined for each sub-carrier, for each signal path a control unit 195 assigns the sub-carriers to one of the constellation groups. Each modulation in each signal path combines data bits to symbols for addressing the constellation points of the respective constellation group and outputs modulated sub-carriers carrying the symbol information d4.
According to embodiments of the invention, each constellation group of the first modulator unit 150, or each modulation is combined with an interleaving process suitable for performing interleaving at bit level, at symbol level or at constellation level in each modulation path, wherein each interleaving process has a variable size and can be adapted to the number of sub-carriers available for the respective constellation group. For instance, symbols of a constellation group might be mapped to various frequency carriers.
A second modulator unit 170 may modulate the sub-carriers carrying the symbol information d4 of the various modulations of each signal path on a main carrier to generate one digital transmission stream d5 for each signal path. These operations may be performed in the frequency domain and an IFT (inverse Fourier transformation) unit 180 may transform the digital transmission streams d5 into the time domain to obtain a digital signal d6 for each signal path. A converter unit 190 may convert the digital signal d6 into analogue transmission signals d7 and couples each analogue transmit signal d7 to one of the transmit ports.
A constellation control unit 195 may receive or derive the channel state information from feedback information that the transmit unit 110 may receive from another communications device with which the transmit unit 110 communicates. In the case the transmit unit 110 is included in a communications device 100 which also includes a receive unit 120 as shown in
For each modulation path the modulator unit 150 includes a modulation unit 154a-f realizing the respective constellation group and using a configurable number of sub-carriers to generate a modulated output signal, which may be, for example, a PSK, a QPSK, a 16-QAM, 64-QAM, 256-QAM, 1024-QAM, a 4096-QAM any other 2n-QAM, or a 2-PAM or any other 2n-PAM signal. Each modulation unit 154a-f uses another one of the constellation groups. The outputs of the modulation units 154a-f represent modulated sub-carriers. The bits contained in the data stream delivered by the grouping unit 152 are mapped to QAM symbols. Dependent on the transmission channel characteristics, each modulation unit 154a-f processes a different number of symbols. Each modulation unit 154a-f is adaptive and programmable with regard to the number and frequency of the used sub-carriers. For example, the constellation control unit 195 may be capable of determining the number and the frequencies of the sub-carriers used in each modulation unit 154a-f according to the current transmission channel characteristics.
In accordance with an embodiment, for each modulator path the interleaving unit 156 includes an interleaver unit 156a that interleaves the sub-carriers in the respective modulator path on constellation level. The interleaver units 156a may be based on pseudo-random number generators, for example shift registers, where the register input is derived from an exclusive- or function of two register cell outputs. The interleaver units 156a are sealable such that each interleaver unit 156a is capable of handling different numbers of sub-carriers in the same constellation group. In this way, the interleaver unit 156a can be combined with adaptive modulation units 154a-f and each interleaver unit 156a can be controlled according to the mode of that modulation unit 154a-f it is assigned to.
In each signal path 131, 132, a degrouping unit 158a may recombine the frequency interleaved sub-carrier groups of the QAM modulator paths, where the interleaved sub-carrier groups are reordered at their original positions, but where the sub-carriers in each of the QAM constellation groups are spread due to the interleaving process. As a result, frequency diversity is increased significantly. Increased frequency diversity improves system bit error performance, especially in case of narrowband interferers. The scalability of the interleaver units 156a allows the combination with an adaptive OFDM system.
In accordance with another embodiment, the modulator unit 150 may include one single modulation unit, which can be over sampled to process the group of carriers serially instead of parallelly as in the preceding embodiment. The symbols of each constellation group can be mapped to various frequency carriers. In a MIMO system, the various carriers of a constellation group can be split to different communication paths.
The transmitter unit 110 of
Each single of a plurality of sub-carriers is assigned to none or one of the constellation groups. According to an embodiment, the assignment of sub-carriers to constellation groups is performed in accordance with tonemap information describing frequency dependent characteristics of the current transmission channel. A constellation control unit 195 may receive and manage the tonemap information.
In each modulator path an interleaver unit 156b may interleave the data bits in the respective modulator path before the data bits are grouped to symbols, or may interleave the symbols before or when they are used to address the various constellation points of the respective constellation group.
In each signal path 131, 132 a modulation units 154a-f is provided for each constellation group. Each modulation unit 154a-f uses a configurable number of sub-carriers and the interleaved data bits or symbols to generate modulated sub-carriers carrying the symbol information, and may be capable of using a PSK, QPSK, a 16-QAM, 64-QAM, 256-QAM, 1024-QAM, a 4096-QAM, any other 2n-QAM or any 2n-PAM scheme, by way of example. Each modulation unit 154a-f uses another one of the constellation groups. Each modulation unit 154a-f is adaptive and programmable with regard to the number and frequencies of the used sub-carriers. For example, the constellation control unit 195 may be capable of determining the number and the frequencies of the sub-carriers used in each modulation unit 154a-f according to the current transmission channel characteristics.
The interleaver units 156b are scalable such that each interleaver unit 156b is capable of handling different number of sub-carriers. Therefore the interleaver units 156b can be combined with the adaptive modulation units 154-f, wherein each interleaver unit 156b is controlled in accordance with the mode of the respectively assigned modulation unit 154a-f.
In each signal path 131, 132, a degrouping unit 158a may recombine the interleaved sub-carrier groups of the modulator paths of each signal path 131, 132, wherein the interleaved sub-carrier groups are reordered into their original positions, but wherein the sub-carriers of the different constellation groups are spread due to the frequency interleaving.
The transmitter unit 110 of
Each sub-unit of the transmit unit 110 may be realized in hardware, software or as a combination thereof. In accordance with embodiments, at least some of the sub-units of the transmit unit 110 are realized as digital signal processing circuits integrated in an integrated circuit. According to other embodiments the transmit unit is a software module of a simulation program.
The diagrams of
In accordance with the illustrative example, sub-carriers whose SNR fall in a first range 401 are assigned to a 4096-QAM modulation path, sub-carriers whose SNR fall in a second range 402 are assigned to a 1024-QAM modulation path, sub-carriers whose SNR fall in a third range 403 are assigned to a 256-QAM modulation path, sub-carriers whose SNR fall in a fourth range 404 are assigned to a 64-QAM modulation path, sub-carriers whose SNR fall in a fifth range 405 are assigned to a 16-QAM modulation path, and sub-carriers whose SNR fall in a sixth range 406 may be assigned to a QPSK modulation path or may be omitted for transmission.
The modulation units 154a-f may use orthogonal constellations. According to other embodiments, each of the modulation units 154a-f may use a rotated constellation. Rotated constellations allow two different PAM (phase amplitude modulation) decoders instead of a single QAM modulator.
Use of rotated constellations in connection with frequency interleaving allows significant performance improvement for multipath and so-called eraser channels.
In contrast, with the rotated constellation of
A second demodulator unit 260 includes a plurality of QAM demodulators using different constellation groups for each digital data stream r3. The second demodulator unit 260 includes for each digital data stream r3 and for each constellation group a scalable de-interleaver unit capable of de-interleaving the data streams r3 in accordance with an interleaving mechanism used on the transmission side. A demultiplexer unit 270 may recombine the two or more demodulated signals r5 to a combined receive signal r6 and a forward error correction unit 280 may use code redundancy included in the signal on the receiver side for detecting and correcting data errors in a receive signal r7.
According to an embodiment, each de-interleaver unit reverses an interleaving process performed on the transmitter side on constellation level. In accordance with other embodiments, each de-interleaver unit reverses an interleaving process performed on the transmitter side on bit or symbol level. According to further embodiments the receive unit 220 comprises a further mapping unit for reversing an inter-output diversity in the transmission signal as discussed above with regard to the combined degrouping units 158a in
Each sub-unit of the receive unit 220 may be realized in hardware, software or as a combination thereof. In accordance with embodiments, at least some of the sub-units of the receive unit 220 are realized as digital signal processing circuits integrated in an integrated circuit.
In accordance with an embodiment, the modulated sub-carriers carrying the symbol information are interleaved at constellation level. According to another embodiment the data bits mapped to the respective constellation group are interleaved at bit level before the data bits are grouped to symbols used for addressing constellation points of the respective constellation group. According to further embodiments, symbols formed by groups of data bits are interleaved before or when the symbols are mapped to the sub-carriers assigned to the respective constellation group.
Schneider, Daniel, Stadelmeier, Lothar, Schwager, Andreas
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